The present invention relates to a direction sensor or a flux sensor, and in particular, relates to such a sensor for finding the direction of earth magnetism at a particular point. The sensor may be used for finding not only the direction but also the location of the particular point on the earth.
The present invention is applicable to locate an automobile.
A prior earth magnetism flux sensor has been shown in Japanese utility model publication 30411/84, and in an article entitled "Magnetic Field Sensor and Its Application to Automobies" in page 83-90, Society of Automotive Engineers, Inc, 1980.
A prior earth magnetism flux sensor is shown in FIG. 1. In the figure, the detector DET has an O-ring shaped magnetic core C made of permalloy, on whic an exciting coil C.sub.D is wound. A pair of detections coils C.sub.x and C.sub.y which are perpendicular to each other are also wound on the core C so that the core C is completely included in those coils C.sub.x and C.sub.y as shown in the figure. The exciting coil C.sub.D is wound along the path of the flux in the core C as shown in the figure. The oscillator OSC provides a signal of the frequency f (for instance f=500 Hz -2 kHz) to the exciting coil C.sub.D. A signal having a double frequency 2f is induced in the coils C.sub.x and C.sub.y according to the horizontal component of the earth's magnetism. The outputs of those coils C.sub.x and C.sub.y are applied to the respective synchronous detectors SYNC through respective bandpass filters BPF and respective amplifiers AMP. The synchronous detectors SYNC also receive the reference signal of the frequency 2f which is provided by said oscillator OSC through a frequency doubler DOUBLER and phase controller (PHASE CONT). The synchronous detectors SYNC provide a direct (DC) signal, the level of which relates to the amplitude of the double frequency 2f signal of the coils C.sub.x and C.sub.y. Those DC signals are applied to DC amplifiers AMP, which provide respective outputs E.sub.x and E.sub.y, relating to the direction of the coils C.sub.x and C.sub.y.
The level of the outputs E.sub.x and E.sub.y depends upon the horizontal component of the earth's magnetism. When the detector DET rotates in the horizontal plane, the output level E of the signals E.sub.x and E.sub.y changes as shown in FIG. 2, in which the horizontal axis shows the direction (.theta.), and the vertical axis shows the level E. The curves are sinusoidal as shown in the figure.
However, the device of FIG. 1 has the following disadvantages. First, the detector DET which must have a ring core is too large in size for practical use (For instance, a prior detector has a diameter of 20-30 mm, and a thickness of 5-10 mm). Further, in the manufacturing process of a detector, it takes a long time to wind a coil on a ring shaped core. An automatic winding on a ring shaped core is impossible. A permalloy core is easily broken by vibration and/or shock. Further, the low exciting frequency is unstable, and therefore, the output levels E.sub.x and E.sub.y are subject to drift over a period of time. The use of a high frequency is also impossible when a permalloy core is used.